Truss component saws in the prior art have generally taken the form of a horizontal base frame on which are mounted a first set of one or more saws in a stationary frame at one end of the base frame and a second set of saws mounted in a movable carriage which can be reciprocated along the base frame. The horizontal movement of the carriage permits truss components of differing lengths to be produced.
A feed-in conveyor system is also provided on the component saw for the controlled feeding of lengths of lumber into the saw blade sets. A waste conveyor is arranged in the base to carry off sawdust and the cut off portions.
U.S. Pat. No. 4,277,993 to Mayo shows this type of a component saw wherein a pantograph movement linkage is provided for rotating each of the circular saw blades about a full 180.degree. movement about the axis of a chord on each of the saw blades. The chords on the saw blades in each set are positioned along a common pivot axis. In this U.S. patent angular movement of each of the saw blades is controlled by the pantograph movement linkage which is in turn powered by a gear movement which is not further described. Each of the saw blades is also vertically movable by manual adjustment through a top crank handle. The saw blades thus move vertically and rotate about the pivot axis so that only two degrees of movement are provided. This limited two degrees of movement of the saw blade in different directions restricts the type of cuts which can be made by this saw apparatus. The absence of an automated angular positioning system on this saw then requires excessive adjustment and set up time expenditure for each type of component which is run through the saw.
U.S. Pat. No. 4,476,684 to Thorsell shows an apparatus for supporting two circular saw blades for cutting wooden trusses which also employs a pantograph linkage. Means are provided in this saw for making minor additional positioning adjustments manually by use of several bolt and slot arrangements. Such adjustment means are not useable when switching from one component cut to the next in a series of such cuts which are normally made during truss component production. A vertical adjustment for the saw mounting is also provided on this unit. No automated saw adjustment mechanism is provided for making high speed adjustments.
Other component saws in which pantograph linkages are employed for achieving various angular settings of the circular saws are U.S. Pat. Nos. 3,229,732 and 3,380,494 both to Mayo.
U.S. Pat. No. Re 25,715 to Mayo shows a four saw truss component machine which has segmental gear indicia scales and pointers for displaying angular positions. One or more of the saws are also provided with a vertical adjustability feature through a manually operated screw crank.
Other similar saw machinery is disclosed in U.S. Pat. Nos. 3,665,982 to Kvalheim; 3,952,620 to Adams and 4,131,143; 4,316,400 and 3,085,895 all to Mayo.
U.S. Pat. No. 3,662,795 to Heflin shows an apparatus for forming stakes in which various angular settings are employed for circular saws. U.S. Pat. No. 4,293,011 to White et al describes a rafter cutting machine.
The truss component saws employed in the industry have not provided for automated angular positioning of the saw blades which is needed if the set up time between successive component cuts is to be minimized for higher productivity in the truss manufacturing business. Also the range of component cuts which can be made on these existing saws is restricted due to the low number of degrees of freedom within which the saw blades can be moved.
The production of building trusses is now evolving into a computer aided design and computer aided manufacturing (CAD/CAM) production process. A builder specifies particular configurations for a given building job such as the needed length and pitch for a series of roof trusses. The truss manufacturer is then responsible for designing the appropriate trusses, cutting the truss components and assembling the same. The truss manufacturer then programs a given truss order through the plant with the aid of computer generated information so that each of the varying components of the truss can be serially produced on one or more component saws without the buildup of large inventories of given truss components. It is now becoming essential for the profitability of such truss manufacturers that large inventory levels for the truss components not accumulate but rather that all components cut in a particular run be immediately used for fabrication. This required low inventory practice then requires the component saws to be adjusted quickly to different angular positions for the successive components which must be produced prior to fabrication of a given job order which may range from 20 to 30 different components in amounts ranging from about 10 to 500 pieces.
The angular adjustability of the component saw blades is presently accomplished largely by hand setting operations wherein scales and pointers are provided so that the operator can properly position each of the saw blades. Such scale and pointer systems are generally accurate to within a range of several degrees. More importantly, valuable production time is expended in achieving the angular settings which must be made for the successive series of component cuts in order to fill a particular job order. When the set up and adjustment time is a high proportion of the total sawing time productivity is unacceptably low. The evolving commercial practice of filling given building job orders in a single production run makes such manual adjustments unacceptable.
It is therefore important to achieve a fast angular positioning and low set up time for each of the successive components to be run through the machine.
In addition to the requirement that the set up and adjustment time between successive cutting runs for the truss components be held to a minimum in order to increase productivity it is also necessary to make a wide range of different angular cuts. It is insufficient to merely provide for the saws to pivot across a large angular range such as 180.degree. or even 360.degree.. In order to make certain cuts such as long scarf cuts it is necessary not only to angularly position the saw blade but to then move the saw blade radially with respect to the pivot axis and to also move the saw along a chord across the blade spaced from the pivot axis. This type of saw blade adjustability has not heretofore been employed in truss component saws. Such additional adjustability for saw blade positioning permits the blades to be adjusted so that the component cuts can be made across long chord lengths of the circular saw blades. This optimises the cutting performance of the blade and permits longer lengths of angular cuts.